Change occurrences of gcc to the more general cc

This is done for the sake of Yosemite, which does not have gcc, and yet
this change is also compatible with Linux.

pkgs/development/libraries/glibc/common.nix

@@ -167,8 +167,8 @@ stdenv.mkDerivation ({
 
     configureScript="`pwd`/../$sourceRoot/configure"
 
-    ${stdenv.lib.optionalString (stdenv.gcc.libc != null)
-      ''makeFlags="$makeFlags BUILD_LDFLAGS=-Wl,-rpath,${stdenv.gcc.libc}/lib"''
+    ${stdenv.lib.optionalString (stdenv.cc.libc != null)
+      ''makeFlags="$makeFlags BUILD_LDFLAGS=-Wl,-rpath,${stdenv.cc.libc}/lib"''
     }
 
     ${preConfigure}

pkgs/development/libraries/glibc/default.nix

@@ -8,7 +8,7 @@
 , withGd ? false, gd ? null, libpng ? null
 }:
 
-assert stdenv.gcc.gcc != null;
+assert stdenv.cc ? gcc;
 
 let
   build = import ./common.nix;
@@ -33,9 +33,9 @@ in
     # libgcc_s will not be at {gcc}/lib, and gcc's libgcc will be found without
     # any special hack.
     preInstall = ''
-      if [ -f ${stdenv.gcc.gcc}/lib/libgcc_s.so.1 ]; then
+      if [ -f ${stdenv.cc.gcc}/lib/libgcc_s.so.1 ]; then
           mkdir -p $out/lib
-          cp ${stdenv.gcc.gcc}/lib/libgcc_s.so.1 $out/lib/libgcc_s.so.1
+          cp ${stdenv.cc.gcc}/lib/libgcc_s.so.1 $out/lib/libgcc_s.so.1
       fi
     '';